Ink ribbon cartridges for a thermal printer are well known. Typically, the ink ribbon cartridge includes an ink ribbon supply spool and an ink ribbon take-up spool that are rotationally supported parallel to one another in a cartridge housing. The ink ribbon has a repeating series of three different color sections or patches such as a yellow color patch, a magenta color patch, and a cyan color patch. Also, there may be a transparent colorless laminating section or patch immediately after each cyan color patch.
Often, a compression-type spring is interposed between an inner wall at one side of the cartridge housing and one hub end of each spool. The spring urges a spool in one direction along the rotation axis of the spool, to force the opposite hub end of the spool against an inner wall at another side of the cartridge housing. This is done to prevent the spool from being rotated accidentally, such as might occur when the cartridge is jarred, which could cause the ink ribbon to partially unwind from the spool and slacken.
During cartridge assembly in prior art U.S. Pat. No. 4,883,234 issued Nov. 28, 1989 a u-shaped leaf spring is rotationally engaged with one hub end of a spool. The spool, engaged with the leaf spring, is inserted laterally into a housing-half to position the leaf spring against an inner wall at one side of the housing-half. The leaf spring then urges the opposite hub end of the spool against an inner wall at another side of the housing-half.
During cartridge assembly in prior art U.S. Pat. No. 5,110,228 issued May 5, 1992 a spool is inserted laterally into a housing-half to position one hub end of the spool against a resilient member projecting integrally from an inner wall at one side of the housing-half. The resilient member urges an opposite end of the spool against a rotation stopper on an inner wall at another side of the housing-half.